Since single crystal diamond has excellent performance such as high hardness, high thermal conductivity, and high light transmittance, it has widely been used in various products such as a tool including a cutting tool, a grinding tool, and a wear resistant tool, optical components, semiconductors, and electronic components (hereinafter also referred to as “diamond products”).
Single crystal diamond used for diamond products includes natural diamond and synthetic diamond. Natural diamond is considerably varied in quality and an amount of supply thereof is unstable, whereas synthetic diamond of constant quality can be supplied in a stable manner. Therefore, synthetic diamond is often used in the industrial field.
Impurity nitrogen in a crystal is one of primary factors determining performance of diamond. Impurity nitrogen affects many physical properties of diamond such as hardness, toughness, and semiconducting characteristics. For example, it has been known that with lowering in concentration of nitrogen in diamond, hardness of diamond is higher and wear resistance improves, whereas chipping resistance lowers. Therefore, a technique for controlling a concentration of nitrogen in diamond has been developed for obtaining synthetic diamond having desired physical properties.
A method for manufacturing synthetic diamond includes a high pressure high temperature method (HPHT) and chemical vapor deposition (CVD) such as hot filament chemical vapor deposition (CVD), microwave excited plasma CVD, and direct current plasma CVD.
With the high pressure high temperature method, a concentration of impurity nitrogen can be controlled approximately between 1 ppm and 200 ppm by adjusting gettering of nitrogen or conditions for growth during synthesis of diamond.
In CVD, a concentration of nitrogen in a diamond crystal can be controlled approximately between 10 ppb and 5 ppm by adjusting conditions for growth of single crystal diamond (an epitaxially grown layer) on a surface of a substrate.